There are clearly many theoretical advantages to the transdermal delivery of dried or lyophilized drugs instead of commercially available oral or injectable forms of these drugs. Delivery of a drug across the skin of a patient obviates the problems of drug inactivation by gastrointestinal fluids or enzymes, fluctuations in absorption from the gastrointestinal tract, and hepatic first pass inactivation, while also avoiding the inconvenience of injection. However, hitherto proposed devices or methods for transdermal delivery of dried particulate or lyophilized drug agents have not successfully yielded reliable uptake and sustained serum levels of the active agent.
Generally speaking the objective of transdermal drug delivery has been tackled using one of two complementary approaches known in the art. One approach provides formulations of drugs that may be applied to the skin in the form of patches, films or matrices of varying compositions, and the alternative approach utilizes a method of puncturing the skin or otherwise disrupting the impermeable layers of the skin to facilitate the entry of drugs into the systemic circulation.
Transdermal Patches
Patches or matrices almost invariably comprise some type of penetration enhancer and some type of adhesive layer, and are known to cause irritation or edema and to produce non-uniform rates and levels of drug uptake among different patients and different skin types.
There are two prevalent types of transdermal patch design, namely the reservoir type where the drug is contained within a reservoir having a basal surface that is permeable to the drug, and a matrix type, where the drug is dispersed in a polymer layer affixed to the skin. Both types of devices also typically include a backing layer and an inner release liner layer that is removed prior to use.
European Patent Application 0391172 describes a transdermal patch having a matrix composed of a water-insoluble material that contains islands of solid particles of drug in a water-soluble/swellable polymer and an underlayer that controls the amount of water vapor passing from the skin to the matrix. The matrix is said to be activated by water vapor from the skin.
Compositions or devices in the form of specific types of patches adapted for the transdermal delivery of dry powder or lyophilized drugs have been disclosed for example in European Patent Application 912239 to PowderJect Research Ltd. that discloses “Method for providing dense particle compositions for use in transdermal particle delivery”.
Methods for transdermal delivery of powders are also disclosed in U.S. Pat. No. 5,983,135 to Avrahami.
U.S. Pat. No. 4,915,950 to Miranda et al. discloses a method for making a transdermal delivery device comprising laminating an adsorbent source layer to a pharmaceutically acceptable contact adhesive layer, the contact adhesive layer comprised of a material that is permeable to the drug, printing a drug in liquid form onto the adsorbent layer, laminating an anchor adhesive layer to the source layer, and applying a backing layer to the anchor adhesive layer.
Methods for transdermal delivery of Growth Hormone Releasing Peptide (GHRP) are disclosed in WO 98/08492 to Novo Nordisk. Methods for transdermal delivery of growth hormone releasing peptide are also disclosed in conjunction with iontophoresis in scientific publications by Singh et al. (J. Controlled Release, 33, 293-298, 1995); Lau, et al. (Pharmaceutical Research 11, 1742-1746, 1994); Kumar et al. (J. Controlled Release 18, 213-220, 1992); Ellens et al. (Int. J. Pharm. 159, 1-11, 1997). In those publications, the onset of the electrical current induces the influx of GHRP across the skin, and cessation of the current terminates the influx of the peptide.
Transdermal Delivery Apparatus
Electrotransport or iontophoretic drug delivery devices have also been disclosed as being useful for the delivery of dried or lyophilized drugs for which it is anticipated that transdermal delivery would be advantageous. U.S. Pat. Nos. 6,169,920 and 6,317,629 to Alza for example disclose iontophoretic drug delivery apparatus, and U.S. Pat. No. 5,983,130 to Alza discloses an electrotransport agent delivery method and apparatus suitable for ionizable drugs.
U.S. Pat. No. 5,681,580 to Jang et al. discloses a patch-like device for iontophoretic transdermal medication of insulin having a container for holding gel-like insulin, and a power supply for furnishing insulin with electricity.
Electroporation is also well known in the art as a method to increase pore size by application of an electric field. Electroporation is disclosed as a means for transiently decreasing the electrical resistance of the stratum corneum and increasing the transdermal flux of small molecules by applying an electric field to increase the size of existing pores (Chizmadzhev et al., Biophysics Journal, 1998, 74(2), 843-856).
U.S. Pat. No. 5,019,034 to Weaver et al. describes apparatus for applying high voltage, short duration electrical pulses on the skin to produce electroporation.
WO 97/07734 to Eppstein et al. discloses thermal ablation of the stratum corneum using an electrically resistive element in contact with the stratum corneum, such that a high current through the element causes a general heating of tissue in its vicinity, most particularly the stratum corneum, the 10-50 micron thick outermost layer of the skin.
U.S. Pat. Nos. 5,885,211, 6,022,316, 6,142,939 and 6,173,202 to Eppstein et al., which are incorporated herein by reference, describe methods for forming micro-pores in the stratum corneum by heating tissue-bound water above the vapor point with a heat-conducting element, so as to enhance transdermal transport of an analyte or active agent. Further enhancement techniques include the use of sonic energy, pressure, and chemical enhancers. For example, U.S. Pat. No. 6,002,961 to Mitragotri et al. discloses a method that includes a simultaneous application of ultrasound and protein on the skin in order to deliver therapeutic doses of proteins across the skin into the blood.
U.S. Pat. No. 3,964,482 to Gerstel, U.S. Pat. No. 6,050,988 to Zuck, and U.S. Pat. No. 6,083,196 to Trautman et al. describe other apparatus and methods for facilitating transdermal delivery of an agent.
U.S. Pat. No. 6,148,232 to Avrahami, which is incorporated herein in its entirety by reference, describes apparatus for applying electrodes at respective points on skin of a subject and applying electrical energy between two or more of the electrodes to cause resistive heating and subsequent ablation of the stratum corneum primarily in an area intermediate the respective points. Various techniques for limiting ablation to the stratum corneum are described, including spacing of the electrodes and monitoring the electrical resistance of skin between adjacent electrodes.